Drive shaft seal for a medical electrical lead

ABSTRACT

A medical electrical lead that includes a lead body having a lead body lumen and an electrode head assembly having an inner wall and an electrode head assembly lumen adjacent to the lead body lumen. The lead further includes a drive shaft that extends through the lead body lumen and the electrode head assembly lumen, and a sealing member, having an outer diameter corresponding to the inner wall of the electrode head assembly lumen. The sealing member includes an inner lumen that receives the drive shaft, an outer sealing member that is fixedly engaged with the inner wall of the electrode head assembly, and an inner sealing member engaged with the drive shaft to provide a low friction seal.

REFERENCE TO PRIORITY APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/284,430 filed on Apr. 17, 2001, entitled “MEDICAL ELECTRICAL LEAD”,incorporated herein by reference in its entirety.

CROSS-REFERENCE TO RELATED APPLICATIONS

Cross-reference is hereby made to commonly assigned related U.S.Applications, filed concurrently herewith, entitled “INSULATING MEMBERFOR A MEDICAL ELECTRICAL LEAD AND METHOD FOR ASSEMBLY”; P-10012,entitled “IMPLANTABLE MEDICAL LEAD HAVING A RETRACTION STOP MECHANISM”;P-10013, entitled “APPARATUS FOR TRANSFERRING TRACTION FORCES EXERTED ONAN IMPLANTABLE MEDICAL LEAD”; and P-10051, entitled “MEDICAL ELECTRICALLEAD”.

FIELD OF THE INVENTION

The present invention relates generally to a medical electrical lead,and, more particularly, the present invention relates to an implantablelead having a seal for preventing the ingress of body fluids into thelumen of a lead body.

BACKGROUND OF THE INVENTION

A wide assortment of implantable medical devices (IMDs) are presentlyknown and in commercial use. Such devices include cardiac pacemakers,cardiac defibrillators, cardioverters, neurostimulators, and otherdevices for delivering electrical signals to a portion of the bodyand/or receiving signals from the body. Pacemakers, for example, aredesigned to operate so as to deliver appropriately timed electricalstimulation signals when needed, in order to cause the myocardium tocontract or beat, and to sense naturally occurring conduction signals inthe patient's heart.

Devices such as pacemakers, whether implantable or temporary externaltype devices, are part of a system for interacting with the patient. Inaddition to the pacemaker device, which typically has some form of pulsegenerator, a pacing system includes one or more leads for deliveringgenerated signals to the heart and for sensing cardiac signals anddelivering those sensed signals from the heart back to the pacemaker. Asis known, pacemakers can operate in either a unipolar or bipolar mode,and can pace the atria or the ventricles. Unipolar pacing requires alead having only one distal electrode for positioning in the heart, andutilizes the case, or housing of the implanted device as the otherelectrode for the pacing and sensing operations. For bipolar pacing andsensing, the lead typically has two electrodes, one disposedsubstantially at the distal tip end of the lead, and the other spacedsomewhat back from the distal end. Each electrode is electricallycoupled to a conductive cable or coil, which carries the stimulatingcurrent or sensed cardiac signals between the electrodes and theimplanted device via a connector.

Combination devices are available for treating cardiac arrhythmias thatare capable of delivering electrical shock therapy for cardioverting ordefibrillating the heart in addition to cardiac pacing. Such a device,commonly known as an implantable cardioverter defibrillator or “ICD”,uses coil electrodes for delivering high-voltage shock therapies. Animplantable cardiac lead used in combination with an ICD may be aquadrapolar lead equipped with a tip electrode, a ring electrode, andtwo coil electrodes. A quadrapolar lead requires four conductorsextending the length of the lead body in order to provide electricalconnection to each electrode.

In order to perform reliably, cardiac pacing leads need to be positionedand secured at a targeted cardiac tissue site in a stable manner. Onecommon mechanism for securing an electrode position is the use of arotatable fixation helix. The helix exits the distal end of the lead andcan be screwed into the body tissue. The helix itself may serve as anelectrode or it may serve exclusively as an anchoring mechanism tolocate an electrode mounted on the lead adjacent to a targeted tissuesite. The fixation helix may be coupled to a drive shaft that is furtherconnected to a coiled conductor that extends through the lead body asgenerally described in U.S. Pat. No. 4,106,512 to Bisping et al. Aphysician rotates the coiled conductor at a proximal end to causerotation of the fixation helix via the drive shaft. As the helix isrotated in one direction, the helix is secured in the cardiac tissue.Rotation in the opposite direction removes the helix from the tissue toallow for repositioning of the lead at another location.

When using such a lead, it is desirable to prevent the ingress of bodyfluids into the lead body. Blood or other body fluids entering the leadbody can create a pathway for infection, a serious complication forimplantable devices. Furthermore, the entrance of blood into the lumenof a lead body can interfere with the insertion of a stylet used forlead positioning during implantation and with the final connection ofthe lead to an implantable medical device.

Methods for sealing the distal end of the lead body while still allowinga coiled conductor and drive shaft to rotate for advancing or retractinga fixation helix are known. One method is to provide a sealing membranewithin the lumen of the distal lead tip. Reference is made to U.S. Pat.No. 4,311,153 issued to Smits. When the helix is advanced, the pointedtip of the fixation helix punctures the sealing membrane, which providesa seal around the fixation helix. When used during implantation,multiple turns of the coil may be required in order to build up torqueto overcome the friction encountered when rotating the helix through themembrane. The helix may not advance by the same amount with each turnapplied to the coil. Therefore, the extension or retraction of the helixmay be somewhat unpredictable. The punctured membrane may not alwaysform a fluid-tight seal around the fixation helix.

Another method for sealing the lumen of a medical lead involvespositioning a sealing ring to encircle the drive shaft connected to thefixation helix. This type of seal may be maintained in a desiredlocation by retainers mounted proximal and distal to the seal. Referenceis made to U.S. Pat. No. 5,948,015 issued to Hess et al.

Pacemaker systems, as well as other medical devices such as thosementioned above, can utilize a wide variety of lead designs. Manyconsiderations are taken into account when optimizing the design of alead. For example, minimizing lead size is important since a smallerdevice is more readily implanted within the cardiac structures orcoronary vessels of a patient. Moreover, providing features that make alead easier to implant and extract allows the clinician to complete theassociated surgical procedure more safely and in less time. Finally, anoptimized lead design requires a minimum number of parts that may beassembled using techniques that are relatively simple and low cost.

A medical lead having an improved seal against body fluids and whichallows precise control over the rate of advancement of a fixation helixis therefore needed. Furthermore, such a seal should not requiredifficult or costly lead manufacturing techniques. The improved sealpreferably is capable of withstanding the high pressures encounteredwithin the heart so that, when the lead is used in conjunction withimplantable pacemakers or ICDs, blood does not enter the lead lumen andinterfere with the implant procedure or cause infection.

SUMMARY OF THE INVENTION

The present invention is directed to a medical electrical lead thatincludes a lead body having a lead body lumen and an electrode headassembly having an inner wall and an electrode head assembly lumenadjacent to the lead body lumen. The lead further includes a drive shaftthat extends through the lead body lumen and the electrode head assemblylumen, and a sealing member, having an outer diameter corresponding tothe inner wall of the electrode head assembly lumen. The sealing memberincludes an inner lumen that receives the drive shaft, an outer sealingmember that is fixedly engaged with the inner wall of the electrode headassembly, and an inner sealing member engaged with the drive shaft toprovide a low friction seal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an implantable cardiac lead utilized inaccordance with the present invention;

FIG. 2 is a sectional view of a multi-lumen lead body of the lead shownin FIG. 1;

FIG. 3 is a side cut away view of a distal end of the lead shown in FIG.1;

FIG. 4 is a perspective view of a drive shaft seal according to thepresent invention;

FIG. 5 is a sectional view of a drive shaft seal according to thepresent invention;

FIG. 6 is a plan view of a drive shaft and drive shaft seal used inassembling the distal end of the lead shown in FIG. 3.

FIG. 7 is a side, cut-away view of the drive shaft seal shown in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a plan view of an implantable cardiac lead utilized inaccordance with the present invention, embodied as a transvenous cardiacdefibrillation lead. As illustrated in FIG. 1, a lead 10 according tothe present invention includes an elongated lead body 12 having aconnector assembly 16 at a proximal end of lead 10 for connecting to animplantable device and an electrode head assembly 14 at a distal end oflead 10 for carrying one or more electrodes. Lead 10 is shown as aquadrapolar lead including a helical tip electrode 30, a ring electrode50, a right ventricular (RV) defibrillation coil 38 and a superior venacava (SVC) defibrillation coil 40. The helical tip electrode 30 and ringelectrode 50 may be utilized to sense cardiac signals and/or deliverpacing pulses to a patient. One of the defibrillation coils 38 and 40serves as the cathode while the other serves as the anode duringdelivery of a defibrillation shock to a patient as a result of adetected tachycardia or fibrillation condition.

The lead body 12 takes the form of an extruded tube of biocompatibleplastic such as silicone rubber. Multiple lumens located within the leadbody 12 carry four insulated conductors from the connector assembly 16to the corresponding electrodes 30, 50, 38 and 40 located at or near thedistal end of the lead 10. The multi-lumen lead body 12 may correspondgenerally to that disclosed in U.S. Pat. No. 5,584,873 issued to Shoberget al. Three of the insulated conductors carried by lead body 12 arestranded or cabled conductors, each electrically coupled to one of thering electrode 50, the RV coil 38 and the SVC coil 40. The cabledconductors may correspond generally to the conductors disclosed in U.S.Pat. No. 5,246,014, issued to Williams et al., incorporated herein byreference in its entirety. A fourth, coiled conductor extends the lengthof the lead body 12 and is coupled to the helical tip electrode 30.

In this embodiment, the helical tip electrode 30 functions as anelectrode for cardiac pacing and/or sensing and as an active fixationdevice for anchoring the lead 10 in a desired position. In otherembodiments that may employ the present invention, a helical tip mayfunction only as an active fixation device. Reference is made to U.S.Pat. No. 4,217,913 to Dutcher, incorporated herein by reference in itsentirety. Therefore, the helical tip electrode 30 may also be referredto herein as a “fixation helix.”

The connector assembly 16 has multiple connector extensions 18, 20, and22 arising from a trifurcated connector sleeve, typically formed ofsilicone rubber. The connector extensions 18, 20, and 22 couple the lead10 to an implantable medical device such as an implantable cardioverterdefibrillator (ICD).

Connector extension 20 is shown as a bi-polar connector including aconnector ring 24 and a connector pin 25. Connector extension 20 housesthe cabled conductor that is electrically coupled to the connector ring24 at its proximal end and to the ring electrode 50 at its distal end.The connector extension 20 also houses the coiled conductor that iselectrically coupled to the connector pin 25 and extends to the tipelectrode 30. During a lead implant or explant procedure, rotation ofthe connector pin 25 relative to the connector assembly 16 causescorresponding rotation of the coiled conductor and advancement orretraction of the helical tip electrode 30 in the fashion generallydescribed in U.S. Pat. No. 4,106,512 to Bisping et al., incorporatedherein by reference in its entirety. By advancing the helical tipelectrode 30, the electrode 30 can be actively fixed in cardiac tissue.A stylet 32 may be advanced within an inner lumen of the coiledconductor to the distal end of the lead 10 to aid in lead placementduring an implant procedure.

The connector extension 18 carries a single connector pin 52 that iselectrically coupled to an insulated cable extending the length of thelead body 12 and electrically coupled to the RV coil 38. The connectorextension 22 carries a connector pin 42 that is electrically coupled toa respective insulated cable that is further coupled to the SVC coil 40.

FIG. 2 is a cross-sectional view of a multi-lumen lead body of the leadshown in FIG. 1. As illustrated in FIG. 2, lead body 12 includes fourlumens 102, 122, 124, and 126. Lumen 102 carries the coiled conductor26. The conductor 26 is shown surrounded by an insulation tubing 120. Astylet 32 may be advanced within the lumen 34 of the coiled conductor26. Lumen 122 carries an insulated cable 110 that is electricallycoupled at a proximal end to the connector ring 24 and at a distal endto the ring electrode 50. Lumen 124 carries an insulated cable 112 thatis electrically coupled at a proximal end to the connector pin 52 and ata distal end to the RV coil 38. Lumen 126 carries an insulated cable 114that is electrically coupled at a proximal end to the connector pin 42and at a distal end to the SVC coil 40.

FIG. 3 is a side cutaway view of the distal end of the lead 10 showing adetailed view of the electrode head assembly 14 and the electrodes 30,50 and 38. The molded, tubular electrode head assembly 14 includes twomembers, a distal electrode head assembly 113 and a proximal electrodehead assembly 111. The distal and proximal electrode head assemblies 113and 111 are preferably formed from a relatively rigid biocompatibleplastic. For example, assemblies 113 and 111 may be fabricated frommolded polyurethane. The proximal electrode head assembly 111 is coupledto the multi-lumen lead body 12, typically formed from a relatively morecompliant plastic such as silicone rubber, at a joint 140. The lumen 104within the proximal electrode head assembly 111 communicates with thelumen 102 within the lead body 12 for carrying the coiled conductor 26extending between the tip electrode 30 and the connector ring 26. InFIG. 3, the ring electrode 50 is shown coupled to the cable 110, and theRV coil 38 is shown positioned on the outer diameter of the proximalelectrode head assembly 111 and the lead body 12.

FIG. 3 further shows the helical tip electrode 30 electrically coupledto the coiled conductor 26 via a drive shaft 100. The electrode 30 anddrive shaft 100 are preferably fabricated of a biocompatible metal suchas platinum iridium alloy. The coiled conductor 26 extends to theproximal connector assembly 16. Rotation of the connector pin 25 at theproximal end of coiled conductor 26 causes corresponding rotation of thedistal end of the coiled conductor 26 to, in turn, cause rotation of thedrive shaft 100. This rotation results in extension or retraction ofhelical tip electrode 30. A guide 28 actuates the helical tip 30 as itis advanced or retracted. In accordance with the present invention, thelead 10 includes a drive shaft seal 109 encircling the drive shaft 100.The drive shaft seal 109, which may be formed of silicone or any otherelastomer, is housed within the electrode head assembly 14.

FIG. 4 is a perspective view of a drive shaft seal according to thepresent invention. As illustrated in FIG. 4, the drive shaft seal 109includes two outer sealing rings 260 located substantially at each endof the seal 109. It is recognized that any number of outer sealing ringsmay be provided any where along the length of seal 109. These outersealing rings 260 form a high-friction seal with the inner diameter ofthe electrode head assembly 14.

In particular, as illustrated in FIG. 4, an outer diameter 258 of theseal 109 has a “D” shape. This “D” shape, which is also shown by thesectional view of FIG. 5, matches a “D” shaped inner diameter of theelectrode head assembly 14. The seal 109 has a circular inner lumen 252,through which the drive shaft 100 passes. According to the presentinvention, the particular shape of the outer diameter 258 may be of anyshape that corresponds to the inner diameter of the electrode headassembly 14. Interference between the outer diameter 258 and the innerdiameter of electrode head assembly 14 prevents shifting or rotation ofthe seal 109 relative to the electrode head assembly 14 when the driveshaft 100 is rotated within circular lumen 252. The outer sealing rings260 are sized to provide a press fit so that the outer sealing rings 260are fixedly engaged against an inner wall 150 of the lumen 104 ofelectrode head assembly 14, creating a seal along inner wall capable ofwithstanding pressures that may be typically encountered within thecardiovascular system.

FIG. 6 is a plan view of a drive shaft and a drive shaft seal used inassembling a distal end of the lead, according to the present invention.As illustrated in FIG. 6, the drive shaft seal 109 is positioned overthe drive shaft 100 prior to welding the coiled conductor 26 to theproximal portion of the shaft 100. Then the proximal, non-welded end ofthe coiled conductor 26 is inserted in the tubular electrode headassembly 14 as indicated by the arrow 200. The coiled conductor 26 andthe drive shaft 100 are advanced within the electrode head assembly 14until the seal 109 is fit within the electrode head assembly 14, in aposition as shown in FIG. 3. Because the drive shaft seal 109 isretained within the electrode head assembly 14 via a friction fit,assembling the lead 10 with the seal 109 does not require additionalparts or bonding methods. As a result, fewer manufacturing faults occurduring lead production, manufacturing cost is decreased, and theassembly process is made simpler.

FIG. 7 is a side, cut-away view of a drive shaft seal according to thepresent invention. As illustrated in FIG. 7, the shaft seal 109according to the present invention includes two inner sealing rings 250that flexibly conform to the drive shaft 100. The inner sealing rings250 are shown located substantially at each end of the seal 109, but itis recognized that any number of sealing rings may positioned any wherealong the length of the seal 109 within the inner lumen 252. The innersealing rings 250 are shown to be semi-circular in cross-section in FIG.7, however the inner sealing rings 250 may be of any geometrical shapein cross-section, such as square, rectangular or otherwise, that stillprovides an acceptable sealing interface with the drive shaft 100.Likewise, the two outer sealing rings 260 are not limited to having thecross-sectional geometry illustrated in FIG. 7 but could have anygeometrical shape that provides an acceptable sealing interface with thehead electrode head assembly 14.

Because the inner sealing rings 250 provide a low friction seal whenengaged against the drive shaft 100, the drive shaft 100 is allowed torotate without encountering an undue amount of friction. As a result,the coiled conductor 26 used to rotate the drive shaft 100 may beconstructed with smaller, more responsive coils. Smaller coil diameterresults in an overall reduced lead body size. The low friction sealprovided by the inner sealing rings 250 allows for the linear ornear-linear transfer of torque from the proximal end of coiled conductor26 to the helical tip 30, making helix extension easy to control, whilestopping ingress of fluid within the lumen 104 electrode head assembly14, while allowing rotation of the drive shaft 100 within the innerlumen 252.

As illustrated in FIGS. 4 and 7, drive shaft seal 109 includes a distalportion 264 and a proximal portion 266. According to the presentinvention, the drive shaft seal 109 is molded so that the outer sealingrings 260 are form with an outer edge 268 that is square, so thatparting lines 270 corresponding to the distal portion 264 and theproximal portion 266 are perpendicular to an axis 272 extending throughthe inner lumen 252 of the drive shaft seal 109, and the mold usedduring the molding process is parted along the squared outer edge 268.As a result, the drive shaft seal 109 of the present invention providesa robust seal by avoiding potential breaks in the seal at the outersealing rings 260.

In addition, inner sealing rings 250 of the drive shaft seal 109 of thepresent invention are positioned to be aligned with opposite positionedouter sealing rings 260. As a result, the drive shaft 100 exerts a forceon the inner sealing rings 250 which is translated directly to thecorresponding oppositely positioned outer sealing rings 260, while atthe same time inner wall 150 of lumen 104 exerts a force on the outersealing rings 260 which is translated directly to correspondingoppositely positioned inner sealing rings 250. As a result, localizedpressure at the seal formed between the outer sealing rings 260 and theinner wall 150, and between the drive shaft 100 and the inner sealingrings 250 is stabilized, improving the seal formed by the inner sealingrings 250 and the outer sealing rings 260.

The drive shaft seal is formed from a resilient, supple material,preferably silicone rubber. The volume of the seal is made as large aspossible within the available space of the electrode head assembly inorder to increase the compliance of the seal and provide a tightlypressed fit within the electrode head assembly, thereby improving theeffectiveness of the seal. A large surface area on the outer diameter ofthe seal provides interference with the adjacent electrode head assemblycreating a high-friction fit that prevents shifting of the seal. A lowersurface area on the inner diameter of the seal provides a low-frictioninterface with the drive shaft, allowing the shaft to easily rotatewithin the seal.

The present invention thus provides a reliable seal against body fluidsin an implantable medical lead. The seal further provides a low-frictioninterface with a rotatable drive shaft such that less torque is neededto advance the helix than with prior known sealing methods. Thislow-friction interface allows predictable linear advancement of thefixation helix with each turn applied to a coiled conductor. Thelow-friction seal further allows the coiled conductor to be made fromsmaller coils, reducing overall lead size. The seal provided by thepresent invention is easy to assemble since no additional parts orbonding methods are required.

The lead described above employing a drive shaft seal in accordance withthe present invention is a quadrapolar high-voltage lead of the typethat may be used for pacing, cardioversion and defibrillation. However,it will be understood by one skilled in the art that any or all of theinventive aspects described herein may be incorporated into other typesof lead systems. For example, one or more of the aspects of the driveshaft seal described herein may be included in any unipolar ormultipolar pacing lead having a rotatable drive shaft and anycombination of one or more tip, ring or coil electrodes for use inpacing, sensing, and/or shock delivery. Alternatively, any drug-deliveryor other electrical stimulation lead that benefits from having a sealedlumen may employ aspects of the current inventive lead system. As such,the above disclosure should be considered exemplary, rather thanlimiting, with regard to the following claims.

1. A medical electrical lead, comprising: a lead body having a lead bodylumen; an electrode head assembly having an inner wall forming anelectrode head assembly lumen adjacent to the lead body lumen; a driveshaft extending through the lead body lumen and the electrode headassembly lumen; and a sealing member including an outer diametercorresponding to the inner wall of the electrode head assembly, a firstend, a second end, an inner lumen extending from the first end to thesecond end and receiving the drive shaft, a first inner sealing ringpositioned in proximity to the first end and a second inner sealing ringpositioned in proximity to the second end; wherein the first sealingring and the second sealing ring engage the drive shaft in a lowfriction seal, and wherein the sealing member further includes a firstouter sealing ring and a second outer sealing ring, the first sealingring and the second sealing ring forming a high friction seal with theinner wall of the electrode head assembly.
 2. The lead of claim 1,wherein the first outer sealing ring is positioned in proximity to thefirst end of the sealing member, approximately aligned with the firstinner sealing ring, and the second outer sealing ring is positioned inproximity to the second end, approximately aligned with the second innersealing ring.